Vapor generating and superheating installation



July 2, 1957 v o. OLSEN 2,

VAPOR GENERATING AND SUFERHEATING INSTALLATION Filed oct. 11, 1955' INVENTOR.

Oscar Olsen BY ATTORNEY States VAPOR GENERATING AND SUPERHEATING INSTALLATION Application October 11, 1955, Serial No. 539,772 5 Claims. (Cl. 122-480) This invention relates in general to vapor generators and, more particularly, to vapor generating and superheating units of the type including provisions for regularly by-passing heating gases around vapor superheating surface to control the heat absorption thereof.

In a vapor generating and superheating unit of the type of the invention, the amount of convection heated vapor superheating surface is proportioned and arranged to provide a predetermined final vapor temperature at the vapor outlet at a predetermined load. The unit, without the invention, has a vapor outlet temperature curve with a rising characteristic, so that at vapor loads in excess of the predetermined load, the vapor temperature will be above the desired value. As the prime mover usually associated with such a unit is generally designed for operation with a maximum vapor temperature at the predetermined load, provisions are normally made for reducing the vapor temperature to the desired value by controlling the vapor superheating conditions in the unit in such a way that the vapor outlet temperature will not exceed this value.

In accordance with the present invention a vapor generating and superheating unit of the general character described is constructed with a particular arrangement of convection heated vapor superheating surface, whereby the unit can be operated to maintain a substantially constant degree of superheat over a relatively wide vapor generating load range. More specifically, the invention provides means for by-passing furnace gases about vapor superheating surface which includes a bank of vertically extending tubes disposed in the entrance to the high temperature gas zone of an upright main gas pass and transversely of gas flow to these tubes.

The arrangement of vapor superheating surface in the entrance to the main gas pass is such as to provide an optimum rate of heat transfer to this surface and greater compactness of the entire installation.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification, but for a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which a certain specific embodiment of the invention is illustrated and described.

The drawing is a somewhat diagrammatic vertical section of a vapor generating and superheating unit in which a superheater is incorporated in a manner to attain the desired results.

The steam generating and superheating unit illustrated includes a vertically elongated furnace having a heating gas outlet 12 in the upper portion thereof, a secondary superheater section 14, a primary superheater section 16, and an economizer section 18, which are serially arranged with respect to gas flow, in the order named.

The furnace 16 is preferably of rectangular cross-section and defined by walls including steam generating tubes atent 0 2,797,670 Patented July 2, 1957 wholly or partly covered by heat insulating or refractory material, the front wall having a row of tubes 20 extending upwardly from a lower drum 22 to a steam and water drum 24; each side wall having a tube row 26 extending vertically from a bottom header 28 to a top header 30; and the bottom and rear walls having a row of tubes 32 extending from the drum 22 along the furnace bottom and thence upwardly along the rear wall. Some of the tubes 32 have their upper portions inclined upwardly and inwardly toward the wall tubes 20 to define a nose arch 34. Of these arch tubes, some extend vertically from the nose of the arch and, together with tubes 36 extending from a header 38 located in a cavity 40, form a screen 42 disposed forwardly of the secondary superheater section 14. Above the screen these tubes extend forwardly and upwardly along the furnace roof to the drum 24. The remainder of the arch tubes are bent upwardly and rearwardly to define a floor 44 beneath the secondary superheater section 14; then vertically to form, together with upper portions of tubes 46, a screen 48 disposed rearwardly of the secondary superheater section; and then forwardly and upwardly along the furnace roof to the drum 24. The spaces between the upper portions of the floor tubes 44 are closed by flat studs and refractory material.

The remainder of the tubes 32 have their upper portions continuing vertically to form a screen 59 intermediate banks of secondary superheater tubes 52. Above this screen these tubes also extend along the furnace roof to the drum 24.

The steam generating unit shown is of the natural circulation type, feed water being supplied to the upper drum 24 and that drum interconnected to the lower drum 22 by two large diameter downcomer pipes 53 located at opposite sides of the unit. Water is supplied to all of the described wall and screen tuba, except for tubes 36, from the drum 22. Tubes 36 are supplied with water by conduits, not shown, leading directly from the drum 24 to the header 38.

The furnace is fired by burners 54 and the resulting gases pass through the furnace outlet 12 and thence over the furnace screen tubes 42 to the secondary superheater section 14. The secondary superheater section comprises serially connected horizontally spaced banks of multiple-looped vertically arranged superheater tubes 52 disposed on opposite sides of the screen tubes 50. The secondary superheater section is disposed in the laterally extending gas pass which is formed between the inclined floor 44 and the furnace roof so that the height of the pass progressively decreases in the direction of gas flow. While the temperature of the gases decrease in passing over the secondary superheater heating surface, the progressive reduction in the cross-sectional flow area of the pass increases the mass velocity of the gases, (pounds per hour per square foot of cross-sectional area), and thereby maintains a high rate of heat transfer.

Gases leaving the secondary superheater section 14 pass over the tubular screen 48 to an upright convection gas passage 55 and then may flow in entirety horizontally into the upper end of a main gas pass 56; or the gases may divide so as to flow partly through a gas by-pass 58 arranged in parallel with the bottom portion of the main gas pass. Both gas passes are of rectangular cross-section, with all of their walls, except for the wall dividing these passes, defined by superheater supply tubes, the inlets of which are in communication with the steam space of the drum 24. For example, rear wall 60 of the main gas pass includes sections of upright steam tubes 62 and the front wall of the by-pass includes the lower portions of the tubes 46. It will be understood, of course, that all of the gas pass walls above mentioned will have appropriate heat insulating or refractory material associated with the wall tubes so as to close the spaces between the tubes and otherwise complete the wall constructions.

The by-pass 58 and the main gas pass 56 are separated by a division or common wall including economizer outlet tube portions 64', a vertical refractory wall 66 extending across banks of economizer tubes 67 and supported thereby, and a metallic wall 68 suitably secured to and extending downwardly from the bottom of the refractory wall 66 to dampers 70 and 72. A wall 74 forms the front boundary of a by-pass extension 76 which terminates at the dampers 70. A wall 78 forms the rear boundary of a main gas pass extension 80 which terminates at the dampers 72.

The portion of the setting occupied by the main gas pass 56 is of substantial volume and the top portion thereof is advantageously employed for the location of the convection heated primary superheater surface of the unit. The primary superheater section 16 comprises a bank of vertically arranged serially connected return bend tubes 32 disposed across the path of gases at the upper end of the main gas pass. Gases flow from the primary superheater section 16 through a screen 34 formed by economizer outlet tube portions 86 and then turn downwardly 90 to the inlet of the economizer section 18.

With the above described convection gas passage and primary superheater construction and arrangement uniform heating gas distribution to the primary superheater o is assured and substantially all of the space available in the convection gas passage is effectively employed for heat transfer, thus insuring a high degree of unit efficiency and an optimum rate of heat transfer and constant final vapor temperature over a wide range of loads.

The economizer section 18 includes serially connected vertically spaced banks of multiple-looped horizontally arranged economizer tubes 67 extending across the downward flow of gases in the main gas pass and also the by-pass.

The economizer outlet tube portions which define a part of the division wall between the main gas pass 56 and' the by-pass 58 are flat studded and covered with refractory material to prevent the gases from short-circuiting from one pass to the other. These tube portions incline upwardly and inwardly from the top of the refractory wall 66 to a position in line with and beneath the front row of primary superheater tubes 82; and then extend horizontally and rearwardly to define a floor beneath the primary superheater. Above this floor the economizer outlet tubes extend vertically to form the screen 84.

After leaving the economizer section 18 the gases flow over horizontal extensions of the wall tubes 62 to the dampers 70 and 72, and thence to other heat trap equipment, not shown. The dampers 70 and 72 control the gas fiow through the parallel gas passes, permitting variable by-passi'ng of the heating gases around the primary superheater section to provide an effective superheat control over a wide load range. These dampers may be automatically controlled for the purpose of maintaining a predetermined superh'eat temperature, by a control systern which regulates the dampers in accordance with the variations in steam flow from the superheater outlet and also in response to variations in the superheat temperature from a predetermined value.

Lower superheater header 88 is U-shaped with its intermediate section connecting two sides, or legs, one of which is exemplified by a side header portion 90. This header portion is directly connected to an upper header 92 by a row of superheater supply tubes 94. Header 92 receives steam from the drum 24 through tubular connections 96. Itwill be understood that the remaining side wall. of the main gas pass 56 as well. as. that. of. the by-pass 58 is formed by superheater supply tubes con- 4 neeted into the superheater system in the same manner as that just described.

Steam flows from the superheater header 88 through the supply tubes 46 and 62 to a primary superheater inlet header 98. The steam then flows from the inlet header 98 through the upright primary superheater tubes 82 to cross-over tubes 100 which connect the primary superheater tubes to the secondary superheater tubes. From the cross-over tubes steam passes through the secondary superheater tubes 52 to an' outlet header 102, and thence through a conduit, not shown, to the point of use.

Feed water supplied to an economizer inlet header 104, flows upwardly through the banks of tubes 67; and then through the economizer outlet tubes which comprise division wall 64 and screen portions 86, to an outlet header 106. From the header 106 the water flows through two conduits 108 located at opposite sides of the unit to the water space of the drum 24.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

What is claimed is:

1. Apparatus for generating and superheating vapor comprising, in combination, walls lined by spaced vapor generating tubes defining a vertically extending furnace having a heating gas outlet in a wall thereof, walls forming a gas passage opening at one end to said gas outlet, a secondary superheater positioned in said gas passage in the path of gas flow leaving said furnace, walls defining a vertically extending convection gas passage arranged laterally adjacent and opening to the opposite end of said gas passage, means forming a division wall constructed and arranged to provide a main gas pass and a by-pass within said convection gas passage each having an inlet arranged to receive gases flowing from said gas passage, and a primary superheater connected for series steam flow to said secondary superheater and including a bank of upwardly extending tubes disposed in the inlet end of the main gas pass, a portion of said division wall extending transversely of and subjacent to said primary superheater along a substantial portion of the extent thereof in the direction of gas flow across the primary superheater to direct the gases entering the main gas pass in a generally horizontal flow path and to effect uniform gas distribution over the upwardly extending primary superheater tubes.

2. Apparatus for generating and superheating vapor comprising, in combination, walls lined by spaced vapor generating tubes defining an upright elongated furnace having a heating gas outlet in a side wall thereof, walls forming a gas passage opening at one end to said gas outlet, a secondary superheater positioned in said gas passage in the path of gas flow leaving said furnace, walls defining an upright convection gas passage arranged laterally adjacent and opening to the opposite end of said gas passage, means forming a division wall constructed and arranged to provide an upright main gas pass and an upright by-pass within said convection gas passage each having an inlet arranged to receive gases flowing from said gas passage, said by-pass being arranged parallel to and inwardly of the lower portion of said main gas pass, and a primary superheater connected for series steam flow to said secondary superheater and including a bank of upwardly extending tubes disposed in the inlet end of. the main gas pass, a portion of said division wall extending. transversely of and subjacent to said primary superheater along a substantial portion of the extent thereof in the direction of gas flow across the primary superheater to direct the gases entering the main gas pass in a generally horizontal flow path and to effect uniform gas distribution over the upwardly extending primary superheater tubes.

3. Apparatus for generating and superheating vapor comprising, in combination, walls lined by spaced vapor generating tubes defining an upright elongated furnace having a heating gas outlet in a side wall thereof, walls forming a gas passage opening at one end to said gas outlet, a secondary superheater positioned in said gas passage in the path of gas flow leaving said furnace, walls defining an upright convection gas passage arranged laterally adjacent and opening to the opposite end of said gas passage, means forming a division wall constructed and arranged to provide a main gas pass and a bypass within said convection gas passage each having an inlet arranged to receive gases flowing from said gas passage, and a primary superheater connected for series steam flow to said secondary superheater and including a bank of vertically extending tubes disposed in the inlet end of the main gas pass, a portion of said division wall extending transversely of and subjacent to said primary superheater along a substantial portion of the extent thereof in the direction of gas flow across the primary superheater at a position intermediate the upper and lower boundary Walls of said gas passage to direct the gases entering the main gas pass in a generally horizontal flow path and to effect uniform gas distribution over the vertically extending primary superheater tubes.

4. Apparatus for generating and superheating vapor comprising, in combination, walls lined by spaced vapor generating tubes defining an upright elongated furnace having a heating gas outlet in the upper part thereof, walls forming a gas passage opening at one end to said gas outlet, a secondary superheater positioned in said gas passage in the path of gas flow leaving said furnace, walls defining a vertically downwardly extending convection gas passage arranged laterally adjacent and opening to the opposite end of said gas passage, means forming a division wall constructed and arranged to provide a vertically extending main gas pass and a vertically extending by-pass Within said convection gas passage each having an inlet in the upper portion thereof arranged to receive gases flowing from said gas passage, said by-pass being arranged parallel to and inwardly of the lower portion of said main gas pass, a primary superheater connected for series steam flow to said secondary superheater and including a bank of vertically extending tubes disposed in the inlet end of the main gas pass, a portion of said division wall extending horizontally and subjacent to said primary superheater along substantially the entire extent thereof in the direction of gas flow across the primary superheater at a position intermediate the upper and lower boundary walls of said gas passage to direct the gases entering the main gas pass in a generally horizontal flow path and to effect uniform gas distribution over the vertically extending primary superheater tubes, and means for variably controlling the flow of gases through the main gas pass and the by-pass to maintain a predetermined vapor temperature as the vapor generating load changes.

5. Apparatus for generating and superheating vapor comprising, in combination, walls lined by spaced vapor generating tubes defining an upright elongated furnace having a heating gas outlet in the upper part thereof, walls forming a horizontally disposed gas passage opening at one end to said gas outlet, a secondary super heater positioned in said gas passage in the path of gas flow leaving said furnace, walls defining a vertically downwardly extending convection gas passage arranged laterally adjacent and opening to the opposite end of said gas passage, means forming a division wall constructed and arranged to provide a vertically extending main gas pass and a vertically extending by-pass within said convection gas passage each having an inlet in the upper portion thereof arranged to receive gases flowing from said gas passage, said by-pass being arranged parallel to and inwardly of the lower portion of said main gas pass, a primary superheater connected for series steam flow to said secondary superheater and including a bank of vertically extending tubes disposed in the inlet end of the main gas pass, an economized including a bank of vertically spaced tubes disposed below the primary superheater and extending across the downward flow of gases in both the main gas pass and the by-pass, a portion of said division wall including portions of said economizer tubes extending horizontally and subjacent to said primary superheater along substantially the entire extent thereof in the direction of gas flow across the primary superheater at a position intermediate the upper and lower boundary walls of said gas passage to direct the gases entering the main gas pass in a generally horizontal flow and to effectuniform gas distribution over the vertically extending primary superheater tubes, and means for variably controlling the flow of gases through the main gas pass and the by-pass to maintain a predetermined vapor temperature as the vapor generating load changes.

References Cited in the file of this patent UNITED STATES PATENTS 2,553,493 Woolley May 15, 1951 2,608,959 Woolley Sept. 2, 1952 2,681,641 Andrews Jr., et al June 22, 1954 

